This invention relates to sensitive electronic equipment and, more particularly, to an improved arrangement for protecting such equipment from electrostatic discharge.
When a person walks across a carpet, an electrostatic charge can build up on the person's body. This charge can reach a potential on the order of 15,000 volts. If the person approaches a conductive ground path, the charge can jump across a gap between the person's body and the path. In most situations, this does not present any problems. However, if the electrostatic discharge passes through a sensitive electronic component, this can lead to catastrophic failure of the component.
In the past, electronic equipment was typically contained within a metal conductive housing. Therefore, when a person approached the equipment, any electrostatic discharge would jump to the housing and then to ground, bypassing the sensitive electronic components. However, in recent years, more and more such electronic equipment is contained in a plastic insulative housing. The plastic housing eliminates the major path to ground previously provided by the metal housing. With such equipment, there is usually associated one or more fuses which are accessible on the exterior of the plastic housing. One such type of fuse has an indicator window on a visible surface through which can be determined the state of the internal fuse element. Both the window and the remainder of the fuse body are formed of insulative material. The provision of this window results in a small air gap between the window and the rest of the fuse body. Accordingly, an electrostatic discharge can pass through the air gap and reach the internal fuse element, from which it can pass to a sensitive electronic component. Although the electrostatic discharge has a potential on the order of 15,000 volts, its current is very small so that it does not destroy the fuse element. However, the electrostatic discharge possesses enough energy to destroy a sensitive electronic component. It would therefore be desirable to provide an arrangement for preventing an electrostatic discharge from reaching a fuse element within a fuse body.
Attempts in the past to solve this problem have included the placing of a metal door in front of the fuse. However, this obstructs the view of the indicator window. It would therefore be desirable to provide an electrostatic discharge path which does not obstruct the fuse body indicator window.